The Intergovernmental Panel on Climate Change (IPCC) report released by the United Nations on Feb. 2, 2007 states that it is unequivocal that climate change due to global warming is occurring and that it is at least 90 percent certain that humans are responsible. A major cause of this warming is the increased concentration of the “greenhouse gas” carbon dioxide (CO2) in the atmosphere, primarily due to humans burning hydrocarbon fossil fuels to produce energy for transportation and electrical power generation. See FIG. 1. To address the problem of global warming, several countries who are signatories of the Kyoto Protocol agreement are establishing laws to reduce the rate of carbon dioxide emission within their jurisdictions. Several state and local governments in the United States of America are also implementing such laws. One of the legal approaches being used in Europe and elsewhere is a “cap and trade” system. With this approach, decreasing annual limits are set on the total amount of carbon dioxide emitted by each company. Companies that go over their annual cap might be fined. However, efficient companies that emit less than their cap amount earn “carbon credits” that can be sold or traded to excess emitters.
A Feb. 3, 2007, newspaper article by Thomas H. Maugh II and Karen Kaplan of the Los Angeles Times states that the IPCC report “also said warming would continue even in the extremely unlikely event that global carbon dioxide could be stabilized at its current level. Such a stabilization would require an immediate 70 percent to 80 percent reduction in emissions, said Richard Somerville of the Scripps Institution of Oceanography in San Diego.” The carbon dioxide level persists and builds up because the only natural mechanism for “permanently” removing carbon dioxide from the atmosphere is the process of photosynthesis, in which plants use energy from sunlight to convert carbon dioxide and water into plant tissue materials such as sugars and cellulose. The total plant population of the earth cannot consume carbon dioxide at a rate equal to the current rate of carbon dioxide emission from human activities. Carbon dioxide can be “temporarily” removed from the atmosphere when it dissolves in bodies of water such as the ocean, forming carbonic acid. This carbonic acid raises the acidity of the water, endangering the lifeforms living in the bodies of water. Recent “bleaching” of coral reefs has been attributed to this acidification of the ocean, accompanied by the water temperature increases due to global warming. However, if the “carbonated” water warms up or the air pressure above the water is reduced, some of the carbonic acid decomposes and carbon dioxide is released back into the air. An example of this decomposition process is the CO2 bubble formation and “fizzing” which results from the pressure release upon opening a container of a carbonated beverage.
In order to meet CO2 emission reduction targets of present or future regulations such as those based on the Kyoto Protocol, some power generation stations are experimenting with an approach called “carbon sequestration.” In this approach, CO2 gas emitted during the burning of coal or other fossil fuels is trapped at the source and pumped underground. In favorable locations, this gas could be used to pressurize underground petroleum reservoirs, to enhance oil recovery. However, there is no guarantee that the CO2 will not eventually leak back to the surface and re-enter the atmosphere.
There is currently a social movement to develop and deploy “carbon-neutral” technologies for energy generation, technologies that do not emit carbon dioxide. An example of this would be a wind turbine generator. While considerable CO2 might be emitted generating the energy used in manufacturing a wind turbine, when the final device is in operation, no additional CO2 is released. Thus, the manufacturing process may be “carbon-positive” (net CO2 emissions), but the operation of the finished wind turbine is “carbon-neutral”. If the process of manufacturing a second turbine uses an amount of energy equal to the lifetime energy output of the first turbine, then both the manufacturing of the second turbine and its total energy output will effectively be completely “carbon-neutral”. For purposes of this patent application, technologies that are “carbon-neutral” in operation will be referred to as “carbon-neutral” energy sources. Other “carbon-neutral” energy technologies can include solar photovoltaic, solar thermal, hydroelectric, tidal hydroelectric, nuclear, and geothermal.
While the electrical utilities industry is currently developing approaches that may take them at least part way to their CO2 reduction targets, the transportation industry, and particularly airplanes and ocean-going vessels, have more difficult challenges. Vehicles must generally carry their fuel or energy source with them over long distances. Batteries or fuel cells may work for automobiles, once the technology and the “refueling” infrastructure are developed, but these energy sources tend to be heavy, and sometimes bulky. Airlines in particular require light weight, compact, efficient energy sources, and it is difficult to see how fossil fuels and their accompanying CO2 emissions would be replaced in this industry any time soon. Therefore, the airline industry (and others) will be strongly “carbon-positive” for the foreseeable future. In “cap and trade” countries, such industries will be under pressure to buy increasing amounts of increasingly expensive “carbon credits” from other companies. If a “carbon-negative” technology could be developed that would collect CO2 from the atmosphere and convert the carbon to a useful non-gaseous form, the industries that are forced to use fossil fuels could use this CO2 collection/remediation technology to offset their emissions, thereby meeting their net CO2 emission cap targets.
Some preliminary efforts have been made at developing technologies that could chemically convert greenhouse gases such as CO2 into other materials using process that might be considered carbon-negative. See, for example, U.S. Pat. No. 7,140,181, “Reactor for solar processing of slightly-absorbing or transparent gases”, Jensen, et al., and U.S. Pat. No. 6,066,187, “Solar reduction of CO.sub.2”, also by Jensen, et al. However, these are energy-intensive, high temperature processes, requiring intense concentrated sunlight and associated expensive equipment. Furthermore, these patents do not address the problem of collecting the greenhouse gas from the atmosphere and concentrating the gas to make the subsequent chemical reaction processes more efficient.
Other useful related technologies are discussed in the following documents: U.S. Pat. No. 4,478,699, “Photosynthetic solar energy collector and process for its use”, Hallman, et al.; U.S. Pat. No. 4,240,882, “Gas fixation solar cell using gas diffusion semiconductor electrode”, Ang, et al.; and U.S. Pat. No. 4,160,816, “Process for storing solar energy in the form of an electrochemically generated compound”, Williams, et al. These patents also do not address the problem of removing the greenhouse gas from the atmosphere.
Thus, there is a need for a technology capable of collecting a target gas such as CO2 from the atmosphere. The collected target gas may then optionally be converted to other, more desirable forms. There is currently a further need to reduce the concentration of the greenhouse gas CO2 in the earth's atmosphere. The present invention can perform both functions.